Electronic ballast for a discharge lamp

ABSTRACT

An electronic ballast arrangement for a discharge lamp is provided. The electronic ballast arrangement includes an electronic ballast for a discharge lamp with a control application specific integrated circuit, the control application specific integrated circuit having a control input, which is characterized by the fact that the potential present across it sets the operating frequency of the control ASIC when driving the discharge lamp; and a switch; wherein the electronic ballast is connected to the switch, with different switching positions of the switch determining different potentials which are present at the control input, in order to thus set the operating frequency of the control application specific integrated circuit via the switch.

RELATED APPLICATIONS

The present application is a national stage entry according to 35 U.S.C.§371 of PCT application No. PCT/EP2007/061555 filed on Oct. 26, 2007.

TECHNICAL FIELD

Various embodiments relate to an electronic ballast for a dischargelamp.

BACKGROUND

There are electronic ballasts with a large number of levels ofcomplexity. Often, electronic ballasts have a microcontroller. In thecase of such electronic ballasts, configurations are known which make itpossible to dim the discharge lamp. The dimming function is controlledvia a two-core control cable and a dimming potentiometer. Electronicballasts can also include, instead of a microcontroller, a control ASIC(application specific integrated circuit). Such electronic ballasts areless complex. Until now, no electronic ballasts for discharge lamps withcontrol ASIC have been known in which the dimming of the discharge lampis controlled in another way than via a complex circuit with a dimmingpotentiometer.

SUMMARY

Various embodiments provide an electronic ballast for a discharge lampwhich makes it possible to dim the discharge lamp with a compact andinexpensive design in order to be able to possibly thus save energy.

The electronic ballast is connected to a switch via a single-poleterminal, with different potentials being determined at differentpositions of said switch, which potentials are present at a specificcontrol input of the control ASIC. This control input is characterizedby the fact that the potential present across it sets the operatingfrequency of the control ASIC when driving the discharge lamp, i.e. theoperating frequency above which the power is defined during operation(after the switch-on phase). The operating frequency of the control ASICis therefore set via the switch. The operating frequency itself in turndetermines the supply of energy to the discharge lamp. Differentoperating frequencies correspond to different emission powers of thedischarge lamp. In other words, the discharge lamp is dimmed in onestate in comparison with the other state.

In a preferred embodiment, the switch switches a mains connection(preferably a single-core cable) on or off, which mains cable is coupledto the control input of the control ASIC. The switch therefore functionsin binary fashion. This embodiment can be provided in a particularlyinexpensive and compact manner owing to its simplicity. This aspect ofthe invention is based on the knowledge that one advantage of dimming,namely that energy is saved, is also achieved when only a single dimmingpower stage is provided. For example, in the dimmed state 50% of thelight energy can be emitted of the luminous efficiency in the undimmedstate.

In a preferred embodiment, the electronic ballast includes a transistor,whose control input can be connected to the mains connection via theswitch. The binary embodiment can therefore be implemented in a simplemanner with a transistor, i.e. a component part which is particularlyreadily available and inexpensive. Then, a circuit can be influenced bythe transistor, which circuit determines the potential at the controlinput of the control ASIC.

A configuration of the circuit which is particularly inexpensive toimplement is one in which the transistor connects a resistor from thecontrol input of the control ASIC to ground, in particular in parallelwith another resistor. A current or potential in the circuit is alteredby the resistor and is supplied precisely to the control input of thecontrol ASIC.

Discharge lamps are generally preheated at a frequency of around 110kHz, started at a frequency of around 75 kHz and then operated at afrequency of between 40 and 50 kHz if the intention is to emit fullpower. For dimming purposes, a frequency which is between the preheatingfrequency and the starting frequency, for example 85 kHz, is generallyused. In the case of a control ASIC of the type used in the electronicballast according to the invention, it may arise that, if the mainsconnection sets the operating frequency to 85 kHz, the startingfrequency of 75 kHz is not reached after preheating, but the frequencyremains at 85 kHz when it runs down from 110 kHz. In order to preventthis, a terminal of the control ASIC can be used, which terminal can beconsidered to be either the input or the output, and which terminal isat a different potential in the switch-on phase of the discharge lampthan after the switch-on phase. In particular, an output can be usedwhich is used for driving a preheating transformer. This terminal of thecontrol ASIC is coupled to the control input of a transistor, and thedrain output thereof is then coupled to the control input of the firsttransistor. In the switch-on phase, therefore, the further transistor isswitched, and the potential at the control input of the first transistorremains at zero, with the result that in the switch-on phase, thesituation in which the mains connection is switched off is extended.Once the switch-on phase has ended, the switching of the furthertransistor is ended, the mains potential at the control input of thefirst transistor can be formed, and a corresponding potential is thenpresent at the control input of the control ASIC via which the operatingfrequency of the control ASIC is set (after the switch-on phase). Thisensures that the discharge lamp is switched on, i.e. preheated andstarted, in a reliable manner when it is intended to be dimmedimmediately after being switched on.

BRIEF DESCRIPTION OF THE DRAWING(S)

The invention will be explained in more detail below with reference toan exemplary embodiment. The single FIGURE shows a circuit diagram ofthose of the components of the electronic ballast according to theinvention which are essential to the explanation of the invention.

DETAIL DESCRIPTION

The following detailed description refers to the accompanying drawingsthat show, by way of illustration, specific details and embodiments inwhich the invention may be practiced.

In a preferred embodiment of an electronic ballast according to theinvention, the control ASIC ICB1FL02G by Infineon is used for drivingdischarge lamps. The control ASIC has an input “RFRUN”, which serves thepurpose of setting the operating frequency of the control ASIC, i.e. thefrequency which is applied to the discharge lamp, in particular once thedischarge lamp has run through a switch-on phase with preheating andstarting. The operating frequency is set via the potential which ispresent at “RFRUN” or the current which results through the connectedresistor. This voltage drops across a resistor R5 at 11 kΩ. A resistorR4 with a resistance of 13 kΩ, in series with a transistor Q1, isconnected in parallel with the resistor R5. The resistor R4 can beconnected in parallel and switched off via the transistor Q1. Thepotential at the control input “RFRUN” can therefore be influenced viathe transistor Q1. A single switch (for example a toggle switch), viawhich a control potential can be applied to the transistor Q1, is nowconnected to the electronic ballast. This switch is not shown in theFIGURE. It connects an input L2 of the circuit arrangement of theelectronic ballast to a mains potential. The input L2 is connected tothe control input of the transistor Q1 via a resistor R2 with aresistance of 1 MΩ and a diode D1 as well as resistor R3 with aresistance of 10 kΩ. A zener diode D2 can be connected to ground in theoff direction between the resistor R2 and the diode D1 in order todivert interference pulses out of the power supply system. A resistor R1with a resistance of 20 kΩ and a capacitance C1 of 1 nF are connected inparallel with one another and to ground between the diode D1 and theresistor R3.

If no mains potential is present at L2, the transistor Q1 is off, andthe voltage present between RFRUN and GND is determined by R5 alone.When equipping the electronic ballast with components with thecharacteristics illustrated in the FIGURE, once the electronic ballasthas been switched on, said electronic ballast first runs through apreheating phase, in which a frequency of 110 kHz is applied to thedischarge lamp. With a target of a minimum of 3.3 J and a maximum of 5.7J, a preheating energy at a preheating time of 1 s is actually achievedwhich is 3.8 J. After the preheating, the frequency is run down to 75kHz, and starting is introduced. The starting time is 22 ms, and thestarting voltage is 900 Vrms. Then, the actual operation is introduced,to be precise the control ASIC is operated at an operating frequency of43 kHz in order to emit a maximum luminous efficiency. The mains poweris in this case 60.7 W, the lamp voltage is 122 V, the lamp current is457 mA and the lamp power is 55.6 W. At losses of 5.1 W, an efficiencyof 92% is achieved.

If the switch (not shown in the FIGURE) is now switched on, with theresult that the mains voltage is present at the input L2, the transistorQ1 switches on, and the voltage present between the input RFRUN and GNDis determined by the parallel circuit including R5 and R4. In this case,the operating frequency again rises to 85 kHz in order to emitapproximately half the maximum power. The mains power is 36.5 W, thelamp voltage is 167 V, the lamp current is 177 mA and the lamp power is29.4 W. At losses of 7.1 W, an efficiency of 81% is achieved. Anadditional circuit is now also provided in the circuit arrangement ofthe electronic ballast, which additional circuit enables the switch-onoperation when the mains voltage is present at the input L2 prior toswitching on. As described above, the mains potential at the input L2has the effect that the operating frequency is set to 85 kHz. After thepreheating at 110 kHz, the frequency would therefore not be able to rundown to the starting frequency of 75 kHz. A circuit is provided whichdelays the switching-on of the transistor Q1 until a point in time afterthe end of the switch-on phase, i.e. the preheating and the starting.For this purpose, a MOSFET M1 is provided, whose drain output is coupledto a point between the diode D1 and the resistor R3. The gate input ofthe MOSFET is connected to a voltage output VCC of the control ASIC viaa resistor R8 with a resistance of 2.2 MΩ. The control input of theMOSFET M1 is connected to the connection GND via a capacitor C2 with acapacitance of 10 nF, and in addition the control input of the MOSFET isconnected to a connection “RFPH” of the control ASIC via a resistor R7with a resistance of 100 kΩ, said connection for its part beingconnected to the connection “GND” via a resistor R6 with a resistance of11 kΩ. The connection GND is additionally coupled to the sourceconnection of the MOSFET M1. The connection “RFPH” of the control ASICis a connection at which a predetermined potential is present during theswitch-on phase, i.e. the preheating and the starting, which potentialchanges after the switch-on phase. The circuit arrangement is configuredsuch that the MOSFET M1 is switched on during the switch-on phase, withthe result that the point between D1 and R3 is connected to ground.After the end of the switch-on phase, the MOSFET M1 is no longer turnedon, and the potential determined by the input L2 can be set at the pointbetween D1 and R3. If the mains potential is already present at theinput L2 when the discharge lamp is switched on, if desired first thepreheating at a frequency of 110 kHz takes place, then the starting at afrequency of 75 kHz, and subsequently the operating frequency risesagain to 85 kHz in order to achieve dimming operation.

In the case of the electronic ballast according to the invention, adistinction is only drawn between two operating states, namely theemission of full power at an operating frequency of 43 kHz and emissionof 50% power at an operating frequency of 85 kHz. Actuation of theswitch makes it possible to alternate between these states, said switcheffecting or ending the application of the mains potential at the inputL2. The circuit arrangement has a particularly simple design and isparticularly uncomplicated. In contrast to electronic ballasts with amore complex design, it is not possible to set any desired dimmingpower. However, by virtue of the fact that it is possible to alternatebetween emission with maximum energy and emission with 50% energy, anenergy saving mode is provided, and this is sufficient for most energysaving purposes.

Likewise, installation in a luminaire is simplified. Conventionaldimming ballasts are connected via a dedicated two-core control cableand a dimming potentiometer. In the electronic ballast according to theinvention, only one additional core of the mains cable needs to beconnected. Said core is connected to any desired phase of the mainssystem or to the neutral conductor via a mains switch (toggle switch).If the dimming input L2 has not been connected, a maximum power isalways emitted.

While the invention has been particularly shown and described withreference to specific embodiments, it should be understood by thoseskilled in the art that various changes in form and detail may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims. The scope of the invention is thusindicated by the appended claims and all changes which come within themeaning and range of equivalency of the claims are therefore intended tobe embraced.

The invention claimed is
 1. An electronic ballast arrangement for adischarge lamp, the electronic ballast arrangement comprising: anelectronic ballast for a discharge lamp comprising a control applicationspecific integrated circuit, the control application specific integratedcircuit comprising a control input, which is characterized by the factthat the potential present across it sets the operating frequency of thecontrol ASIC when driving the discharge lamp; a switch input selectivelycoupled to a mains potential; a first transistor having a first controlinput, the control input selectively coupled to said mains potential atsaid switch input via a resistor; and a second transistor having, adrain output connected to the control input of the first transistor, anda second control input connected to an input or output of the controlapplication specific integrated circuit which is at a differentpotential in the switch-on phase of the discharge lamp than after theswitch-on phase, wherein connecting said switch input to a mainspotential provides a different potential at said control input than whensaid mains potential is disconnected from said switch input, in order tothus set the operating frequency of the control application specificintegrated circuit.
 2. The electronic ballast arrangement as claimed inclaim 1, wherein the mains connection is provided by a single-corecable.
 3. The electronic ballast arrangement as claimed in claim 1,wherein the first transistor is configured to connect a resistor fromthe control input of the control application specific integrated circuitto ground.